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GPS World

GPS WorldNew testbed for verifying location technologiesInnovation: Evolutionary and revolutionaryGoogle to provide raw GNSS measurementsReceiver Design for the FutureSpeak your mind for a chance at $100BLM’s new GNSS protocols may set undesirable precedentGlobal GNSS Market Trends & Forecasts: Highlights of the GSA GNSS Market Report 2015The Road to Driverless: Autonomous Vehicle Platforms, Sensors and Requirements

http://gpsworld.com The Business and Technology of Global Navigation and Positioning Tue, 12 Jul 2016 00:14:52 +0000 en-US hourly 1 https://wordpress.org/?v=4.5.3 http://gpsworld.com/new-testbed-for-verifying-location-technologies/ http://gpsworld.com/new-testbed-for-verifying-location-technologies/#respond Mon, 11 Jul 2016 11:07:18 +0000

Horizontal indoor accuracy now, elusive z-axis by end of year

At their advent, mobile phones were conceived to be useful for when people were, well, mobile. And in 1996 when the U.S. Federal Communications Commission (FCC) first required that a handset’s location be sent to 911 dispatchers and meet accuracy performance standards, the FCC was understandably solely interested in calls made outdoors.

Indoor FCC rules

(rmnoa357 / Shutterstock.com)

(rmnoa357 / Shutterstock.com)

In recognizing the pervasive use of mobile phones indoors and gains in location-determining technology, last year the FCC adopted new rules that establish accuracy requirements for indoor 911 calls.

The FCC didn’t stop there and tackled vertical positioning, ordering that within six years, the elusive z-axis, or altitude, be added to requirements and meet accuracy standards in cases when there is no dispatchable location. The z-axis is critical in finding a person in a building of more than one story, whether a high-rise apartment building in Brooklyn or a three-story dormitory at a university.

This spring, a testbed for verifying location technologies began operations. The FCC required that nationwide wireless providers create an independently administered and openly transparent test bed to verify location technologies used in meeting the accuracy requirements. CTIA, the trade association for the U.S. wireless communications industry, established the 9-1-1 Location Technologies Test Bed as an independent company.

Testing is designed and administered by ATIS, an industry standards association. The testbed regions are located in metropolitan Atlanta and San Francisco and cover a wide range of building types and terrain.

Indoor testing will be performed in 20 buildings within each test region, spanning four morphology types (dense-urban, urban, suburban and rural). Test bed administrators will not divulge the technologies being tested.

No Silver Bullet. The FCC acknowledges that there won’t be one silver bullet location technology, one size fits all that will be the best location solution in all situations.

In the order released on Feb. 3, 2015, the FCC writes, “To be sure, no single technological approach will solve the challenge of indoor location, and no solution can be implemented overnight. The requirements we adopt are technically feasible and technologically neutral, so that providers can choose the most effective solutions from a range of options.

“In addition, our requirements allow sufficient time for development of applicable standards, establishment of testing mechanisms, and deployment of new location technology in both handsets and networks… Clear and measurable timelines and benchmarks for all stakeholders are essential to drive the improvements that the public reasonably expects to see in 911 location performance.”

The 9-1-1 Location Technologies Test Bed has begun indoor testing of currently deployed horizontal location technologies, and its results will be used as part of location accuracy compliance reporting to meet FCC benchmarks.

Toward the end of this year, location technology vendors will use the Test Bed to test near-term emerging horizontal and vertical location technologies, such as z-axis, that are not currently deployed by the nationwide wireless carriers.

JANICE PARTYKA is GPS World’s contributing editor for wireless. She is principal at JGP Services and provides strategy and marketing consulting to the mobile industry. She reported on a previous round of tests, the 2013 FCC-chartered Communications Security, Reliability and Interoperability Council (CSRIC) trials of NextNav, Qualcomm and Polaris technologies. See gpsworld.com/indoor-trial-results-next-fcc-chief/.

http://gpsworld.com/new-testbed-for-verifying-location-technologies/feed/ 0 http://gpsworld.com/innovation-evolutionary-and-revolutionary/ http://gpsworld.com/innovation-evolutionary-and-revolutionary/#respond Mon, 11 Jul 2016 09:10:02 +0000

The development and performance of the VeraPhase GNSS antenna

By Julien Hautcoeur, Ronald H. Johnston and Gyles Panther

INNOVATION INSIGHTS with Richard Langley

INNOVATION INSIGHTS with Richard Langley

ANTENNAS MATTER. Often overlooked by the casual user of a GNSS receiver, its antenna is a critical component of the system. In the case of consumer equipment such as handheld receivers, satellite navigation units and embedded devices inside smartphones, cameras and fitness monitors, the antenna might not even be visible. Nevertheless, a GNSS antenna must be carefully designed and constructed to maximize the transfer of the electromagnetic energy of the weak GNSS signals into an electrical current that can be fed to the receiver. Typically, this means that the antenna has to be designed for reception of the right-hand circularly polarized signals transmitted by the satellites on their particular frequency or frequencies. Some mass-produced embedded devices might use less efficient linearly polarized antennas coupled with a high-sensitivity receiver simply to shave a few cents off the cost of the units or to fit them into a limited volume. But the pros and cons of such antennas is a discussion for another time.

A GNSS antenna must also be omnidirectional, being able to receive signals arriving from any azimuth and elevation angle with acceptable gain in the hemisphere above the antenna while rejecting those signals arriving from below the antenna that, in most cases, are undesirable reflections off the ground and which have a large left-hand circularly polarized component. Reflected signals from the ground or other surfaces combine with the line-of-sight signals from the satellites resulting in multipath interference, which contaminates pseudorange and carrier-phase measurements. The first line of defense against multipath is a multipath-resistant antenna. Signals from non-GNSS transmitters on nearby frequencies should also be rejected so as not to cause interference to the receiver or overload its front end.

An important characteristic for precision GNSS applications is stable electrical phase centers—the locations in three-dimensional space to which GNSS measurements are referenced. Ideally, they would be perfectly fixed with respect to the antenna housing but, in reality, they will vary with the direction of the arriving GNSS signals. The variation, however, should be small, repeatable and calibrated with the calibration values available for data-processing software.

It was about 40 years ago when the first GPS receiving antennas were developed and there have been many significant advances in antenna design and fabrication since then. You might be tempted to think that there is nothing new in the research and development of GNSS antennas. You would be wrong.

In this month’s column, we take a look at a revolutionary design of a multi-frequency multi-GNSS antenna. Our authors discuss how the antenna evolved from a research project in academia to a commercial product about to enter the market. And, like a number of GNSS advances, it’s Canadian, eh?

The use of GNSS technology has permeated many aspects of life today. With each advancement in the technology, new applications become possible as a result of lowered costs, smaller size, greater capabilities, and higher precision and accuracy. In particular, advances in antenna technology can provide greater capabilities to GNSS receiving equipment.

In this article, we report on the research and commercial development of a high-performance GNSS antenna that can cover all of the GNSS frequency bands, that has high purity circularly polarized radiation, high phase-center stability and high radiation efficiency. Early numerical simulations showed that the turnstile/cup antenna was a good starting point for this research. For GNSS applications, this antenna type required much further research to extend the impedance bandwidth, to reduce cross-polarization and to reduce backward radiation. Many thousands of electromagnetic (EM) computer simulations and optimizations of various circular waveguide (or cup) structures led to a high-performance circularly polarized antenna.

This antenna has excellent axial ratios in all theta and phi directions, low backward radiation, excellent phase-center stability and a compact design. Intermediate and final antenna designs were extensively tested in the anechoic chamber of the Schulich School of Engineering at the University of Calgary. Our company subsequently signed a license agreement with the University of Calgary’s University Technologies International Inc. and undertook further development of the antenna for commercial production. In this article, we present measured results for the resulting commercial antenna known as the Tallysman VeraPhase VP6000 antenna.

Early Circularly Polarized Antennas. One of the first circularly polarized antenna designs (1948) can be attributed to Sichak and Milazzo (see Further Reading), who introduced the turnstile or crossed-dipole circular polarization (CP) antenna. The crossed dipoles must have current flows that are 90 degrees out of phase with each other. This phase difference can be achieved feeding the two dipoles 90 degrees out of phase by a phase-shifting signal splitter or by changing the impedance of each of the dipoles. The turnstile antenna produces highly pure CP only in the two directions normal to the two dipoles. If the dipoles are normal to each other and lie in the horizontal plane, they can radiate right-hand circular polarization (RHCP) upwards while left-hand circular polarization (LHCP) is radiated downwards. At the horizon, they will radiate only a linear horizontally polarized wave. For GNSS applications, this is a serious limitation. By 1973, it was known that a horizontal dipole placed near the open face of a “cup” or shorted waveguide would radiate a linear horizontally polarized wave sideways and a vertically polarized wave in its direction of alignment. These properties were utilized by Epis (see Further Reading) to build a broadband CP antenna.

Research Objective

The university research project began with the objective of developing a high-precision GNSS antenna that would cover all of the frequency bands being considered by the various national GNSS satellite systems, whether launched or under development. It was decided at the onset of the research that computer simulation and optimization methods would be an important part of the research endeavor. Many antenna structures were evaluated using EM simulation tools. Various structures were constructed in software and then simulated. Early simulations indicated that the crossed dipole placed in a cup offered the best possibility for producing a high-performance GNSS antenna. To obtain the best RHCP with minimal LHCP, it became necessary to place the dipoles somewhat within the cup. Nevertheless, the impedance bandwidth of this configuration is insufficient to handle the upper and lower GNSS frequency bands at the same time.

Extending the Antenna Bandwidth. The first structure that was used to handle both the L1 and L2 GNSS bands was a second set of dipoles connected in parallel to the first set. This arrangement provided an adequate match to frequencies close to the L1 band (1575 MHz) and the L2 band (1227 MHz) but it gave a rapidly changing reflection coefficient close to and below the L1 band. The two dipole sets were fed by an appropriate surface-mount 90-degree hybrid coupler designed for the required broad frequency band. The dipoles are fed by microstrip via “grounded legs” that are built on printed circuit board (PCB) technology. Good performance was achieved with this structure, but further improvements in the performance were actively sought. The two dipoles connected directly together cause a deep notch in the radiated signal at a frequency close to and below the L1 band. This was considered to be undesirable. It was decided to use a coupled resonant radiating structure tuned to L1 while the main dipoles would be tuned to L2 (see FIGURE 1).

FIGURE 1. An extended bandwidth GNSS antenna. The lower and connected dipoles are tuned to L2 and the upper coupled shorted dipoles are tuned to L1. Current flow in the circular waveguide of the GNSS antenna is shown. Strong circumferential currents flow at the top of the waveguide. Red indicates large currents and the arrows show the directions of the current flow.

FIGURE 1. An extended bandwidth GNSS antenna. The lower and connected dipoles are tuned to L2 and the upper coupled shorted dipoles are tuned to L1. Current flow in the circular waveguide of the GNSS antenna is shown. Strong circumferential currents flow at the top of the waveguide. Red indicates large currents and the arrows show the directions of the current flow.

It is well known that resonant circuits can be broadbanded by choosing the correct coupling between them. This was tried in software and found to give an excellent wideband response.

Circumferential Current Reduction. Through many EM simulations of the antenna structure, it was found that the LHCP could be suppressed substantially by making the aperture of the cup serrated. The EM wave simulation package allows the user to look at the currents in the structure. The results are shown in FIGURE 2.

FIGURE 2. An antenna with a tapered base and a sawtooth aperture, which reduces circumferential current flow.

FIGURE 2. An antenna with a tapered base and a sawtooth aperture, which reduces circumferential current flow.

The strong circumferential currents (horizontal linear currents) produce radiation with linear horizontal polarization. It is important to reduce the size of these currents to minimize the linearly polarized radiation. The horizontal currents flowing in the top of the waveguide wall are effective in setting up horizontal polarization (HP) radiation in the direction of the horizon. For high-quality CP radiation, the horizontal radiation must be matched by vertical radiation (with a 90-degree phase shift), but the waveguide wall does not permit the required vertical current to flow to produce the vertical polarization (VP) radiation component. Clearly, a serrated waveguide aperture reduces the circumferential current flow. It was also found, through many simulations, that the unwanted polarization components can be reduced by tapering the cup towards the bottom end (see Figure 2).

The sawtooth aperture antenna was chosen for further development. The fed dipoles are constructed using PCB technology and are given shapes that vary from the wire dipole case. The radiating resonator is also constructed using PCB material and is given a different shape from the pure straight-wire case. The software antenna was constructed and tested and found to have good performance with regard to low cross polarization in all directions, low backward radiation and high radiation efficiency.

Further Waveguide Development. It was decided that another way of achieving vertical currents and horizontal currents that would be balanced in magnitude and have a 90-degree phase difference might be obtained by constructing the waveguide walls from a combination of thin conductors connected in a grid. The grid consists of a combination of vertical and horizontal conductors. Simulations with EM software showed the antenna is exceptionally efficient when it uses wires. The wire grid waveguide model of the GNSS antenna was simulated with many, many topological variations. Each variation was optimized for low back (nadir) radiation and high-purity RHCP in all directions. The results were unexpected. The best results were obtained when only one circumferential wire conductor is used and, furthermore, the vertical wire conductors are not connected to the circumferential conductor nor to the base of the antenna. This structure was simulated and optimized many times to derive the best possible topological configuration and component dimensions for a GNSS antenna. A PCB model of the GNSS antenna was then numerically constructed, simulated and optimized as a more practical construction technology for the antenna (see FIGURE 3).

FIGURE 3. The conducting plate waveguide model of the GNSS antenna. The blue plates are conducting sheets and the yellow plates are the dielectric of the PCB.

FIGURE 3. The conducting plate waveguide model of the GNSS antenna. The blue plates are conducting sheets and the yellow plates are the dielectric of the PCB.

Note that the vertical strip conductors do not contact the conducting antenna base. Also note the serrated antenna base, as seen on the inside of the antenna. This design feature reduces excessive circumferential current flow in the base of the antenna. The antenna was tested in the University of Calgary anechoic chamber and in the high-quality Simon Fraser University anechoic chamber (a Satimo SG64), and it was found to have well-suppressed LHCP radiation, very low back radiation and very stable phase centers.

The unique topology of this last antenna provides suppression of the expected downward LHCP radiation that most CP antennas exhibit. Radiation tends to “spill over” from the aperture and travel downwards. Downward radiation also emerges from the gap between the antenna base and the vertical conductors. These two sources of downward radiation are largely out of phase and tend to cancel each other out. This reduced downward LHCP radiation largely removes the need for a choke ring to block the reflections from the ground. This in turn means that the antenna can be compact and light.

Antenna Development

Tallysman's VeraPhase 6000 high-precision GNSS antenna.

FIGURE 4.  Tallysman’s VeraPhase 6000 high-precision GNSS antenna.

We undertook the project of converting the research prototype antenna described above into a commercially viable product. The research prototype antenna was modified to achieve optimized gain at lower GNSS frequencies, high mechanical robustness, adaptation for efficient manufacturability and for use of different materials. This antenna is known as the VeraPhase VP6000 antenna and is shown in FIGURE 4.

The topology of the antenna follows that of the research prototype with dimensional adjustments so as to function correctly with the new materials and circuitry being used. It is light and compact with a diameter of 157 millimeters, a height of 137 millimeters and a weight of less than 670 grams.

VeraPhase Measurements. Anechoic chamber tests were conducted at the Satimo facility in Kennesaw, Georgia, to determine the gain pattern, axial ratio, phase-center offset and variation in multipath-free conditions. Data were collected from 1160 MHz to 1610 MHz to cover all the GNSS frequencies.

Antenna Gain, Efficiency and Roll-off. The chamber measurements show that the VP6000 exhibits a gain at zenith from 4.9 dBic at 1164 MHz to 7.05 dBic at 1610 MHz (see FIGURE 5). This high gain in combination with a wideband pre-filtered low-noise amplifier (LNA) with a noise figure of 2 dB provides for high carrier-to-noise density (C/N0) ratios for all GNSS frequencies. Furthermore, the VP6000 exhibits gain at the horizon from –4.4 dBic at 1164 MHz to –6.8 dBic at 1610 MHz (see Figure 5).

FIGURE 5. RHCP gain of the VP6000 at zenith and the horizon at all GNSS frequencies.

FIGURE 5. RHCP gain of the VP6000 at zenith and the horizon at all GNSS frequencies.

Thus, the gain roll-off from zenith to horizon is between 10.1 dB and 13.6 dB, providing for good tracking at low elevation angles. The radiation efficiency of the VP6000 is 70 percent to 80 percent, corresponding to an inherent (“hidden”) loss of just 1 dB to 1.5 dB, which includes all feedline, matching circuit and 90-degree hybrid coupler losses. In contrast, spiral antennas usually exhibit an inherent efficiency loss of close to 4 dB in the lower GNSS frequencies. Thus, with a high performance LNA, high values of gain translate into higher C/N0 ratios.

FIGURE 6. Normalized radiation patterns of the VP6000 on 60 phi cuts of the GPS frequency bands.

FIGURE 6. Normalized radiation patterns of the VP6000 on 60 phi cuts of the GPS frequency bands.

Radiation Patterns. The radiation pattern of an idealized antenna would have pure CP and constant high gain from zenith down to the horizon and then roll off rapidly for elevation angles below the horizon. In a realizable antenna, the gain should be close to constant over all azimuths for each elevation angle, with strong cross-polarization rejection over that frequency range. The phase-center offset should be stable with minimal phase-center variation. In the upper hemisphere, the greater the difference between the RHCP and LHCP antenna gain, the greater the resistance of the antenna to cross-polarized signals, usually associated with odd order reflections, and hence improved multipath signal rejection. The measured radiation patterns at GPS frequencies are shown in FIGURE 6.

The radiation patterns are normalized to enable direct comparison of the patterns and show the RHCP and LHCP gains on 60 azimuth cuts three degrees apart. The radiation patterns show excellent suppression of the LHCP signals in the upper hemisphere. Similar results were found for all the other GNSS frequencies. The difference between the RHCP gain and the LHCP gain at zenith ensures an excellent discrimination ranging from 31 dB to 53 dB. Also, for the other elevation angles the LHCP signals usually stay 25 dB below the maximum RHCP gain and even 30 dB from 1200 MHz to 1580 MHz. The antenna shows a constant amplitude response to signals coming at a constant elevation angle regardless of the azimuth or bearing angle. This illustrates the excellent multipath mitigation characteristics of the VP6000 at every elevation angle and every GNSS frequency.

Down-Up Ratio. When a direct satellite signal is reflected from the ground, the reflected signal polarization tends to convert, at least partially, from RHCP to LHCP for most soil types. If the terrain underneath the antenna is homogeneous, then the ground surface acts as a mirror, thus providing a reflected signal coming from below the horizon at the negative of the angle of the direct signal above the horizon. Depending on the angle, in part, the field of the inverted and reflected wave adds to the direct wave, which is undesirable. This is the reason, when characterizing the multipath reflection capabilities of an antenna, it is common to use a down-up ratio between antenna gain for LHCP signals for a given angle below the horizon as that for the RHCP signals at the same angle above the horizon. The down-up ratios at L2 and L1 are –25 dB at zenith and they stay under –20 dB for the upper hemisphere, which is usually not the case for standard GNSS antennas. Similar results have been measured over the whole range of GNSS frequencies and confirm the excellent multipath rejection capabilities of the VP6000.

Axial Ratio. The axial ratio (AR) is a measure of an antenna’s ability to reject the cross-polarized portion of a composite signal with both RHCP and LHCP components. Physically, this is an elliptical wave, typically being the combination of the direct and reflected signals from the satellite. The lower the ratio of the major axis to the minor axis of the polarization ellipse, the better the multipath rejection capability of the antenna. To meet operational standards for a multi-band antenna, the axial ratio should meet these requirements at the following elevation angles:

  • 45–90 degrees: not to exceed 3 dB
  • 15–45 degrees: not to exceed 6 dB
  • 5–15 degrees: not to exceed 8 dB.

The worst AR ratio values of the VP6000 at different elevation angles have been plotted in FIGURE 7. The graph shows an AR of less than 0.5 dB at zenith for all GNSS frequencies, and the ARs stay low at all elevation angles down to the horizon. A maximum value of 1.5 dB has been measured for elevation angles above 30 degrees, increasing to just 2 dB at the horizon (0 degree elevation angle) for the worst case azimuth. This performance contributes to the excellent multipath rejection capability of the VP6000.

FIGURE 7. Worst case of axial ratios of the VP6000 at different elevation angles: 90 degrees (zenith), 30 degrees, 10 degrees and 0 degrees (horizon).

FIGURE 7. Worst case of axial ratios of the VP6000 at different elevation angles: 90 degrees (zenith), 30 degrees, 10 degrees and 0 degrees (horizon).

Phase-Center Offset / Phase-Center Variation and Absolute Calibration. For use as a measurement instrument, the antenna must have a precise origin, equivalent to a tape measure zero mark. Thus, it is important that the phase of the waves received by the antenna “appear” to arrive at a single point that is independent of the elevation angle and azimuth of the incoming wave. This point is known as the phase center of the antenna, which should remain fixed for all operational frequencies and for all azimuth and elevation angles of incoming waves, otherwise dimensional measurement is compromised.

In an ideal GNSS antenna, the phase center would correspond exactly with the physical center of the antenna housing. In practice, it varies with the changing azimuth and elevation angle of the satellite signal. The difference between the electrical phase center and an accessible location amenable to measurement on the antenna is described by the phase-center offset (PCO) and phase-center variation (PCV) parameters and their values are determined through antenna calibration.

These corrections are only effective if the predicted phase-center movement is repeatable for all antennas of the same model. The PCO is calculated for each measured elevation angle by considering the signal phase output for all phi (azimuth) values at a specific theta (elevation) angle, and mathematical removal of the normal phase-windup effect in this type of antenna.

A Fourier analysis is then conducted on this resulting data. The fundamental output gives the variation of the horizontal position of the antenna as it is rotated about the z axis. The apparent position normally varies somewhat as the antenna is viewed from various theta angles. The PCV measurement of the VP6000 showed the variation of the phase center in the horizontal plane for elevation angles of 18 to 90 degrees in 3-degree steps at different frequencies. The variations for the different GNSS signals are typically less than 1 millimeter from the x and y axes. Repeatability of the PCO and PCV over several VP6000 antennas has been measured and is also less than 0.5 millimeters.

Five copies of the antenna were sent for absolute calibration by Geo++ in Germany where the VP6000 has been calibrated at GPS L1/L2 and GLONASS G1/G2 signal frequencies. The PCV for the upper hemisphere of the VP6000 at L1 and L2 are plotted in FIGURES 8 and 9. These results confirm a ±1-millimeter PCV at L1 and a ±1-millimeter PCV at L2. Also the standard deviation of the PCV over the five measured antennas stayed under 0.2 millimeters, which represents excellent repeatability. The same results have been observed at G1 and G2.

FIGURE 8. Phase-center variation at L1. The same results have been observed at G1.

FIGURE 8. Phase-center variation at L1. The same results have been observed at G1.

FIGURE 9. Phase-center variation at L2. The same results have been observed at G2.

FIGURE 9. Phase-center variation at L2. The same results have been observed at G2.

LNA and Optional Circuitry. The best achievable C/N0 for signals with marginal power flux density is limited by the efficiency of each antenna element, the gain and the overall receiver noise figure. This can be quantified by a ratio parameter, usually referred to as G/T, where G is the antenna gain (in a specific direction) and T is the effective noise temperature of the receiver — usually dominated by the noise figure of the input LNA.

In the VP6000 LNA, the received signal is split into the lower GNSS frequencies (from 1160 MHz to 1300 MHz) and the higher GNSS frequencies (from 1525 MHz to 1610 MHz) in a diplexer connected directly to the antenna terminals and then pre-filtered in each band. This is where the high gain and high efficiency of the basic VP6000 antenna element provides a starting advantage, since the losses introduced by the diplexer and filters are offset by the higher antenna gain, thereby preserving the all-important G/T ratio.

That being said, GNSS receivers must accommodate a crowded RF spectrum, and there are a number of high-level, potentially interfering signals that can saturate and desensitize GNSS receivers. These include, for example, the Industrial, Scientific and Medical (ISM) band signals and mobile phone signals, particularly Long-Term Evolution (LTE) signals in the newer 700-MHz band, which are a hazard because of the potential for harmonic generation in the GNSS LNA. Other potentially interfering signals include Globalstar (1610 MHz to 1618.25 MHz) and Iridium (1616 MHz to 1626 MHz) because they are high-power uplink signals and particularly close in frequency to GLONASS signals. The VP6000 LNA is a compromise between ultimate sensitivity and ultimate interference rejection.

A first defensive measure in the VP6000 LNA is the addition of multi-element bandpass filters at the antenna element terminals (ahead of the LNA). These have a typical insertion loss of 1 dB because of their tight passband and steep rejection characteristics. Sadly, there is no free lunch, and the LNA noise figure is increased approximately by the additional filter-insertion loss.

The second defensive measure in the VP6000 LNA is the use of an LNA with high linearity, which is achieved without any significant increase in LNA power consumption, by use of LNA chips that employ negative feedback to provide well-controlled impedance and gain over a very wide bandwidth with considerably improved linearity.

Bear in mind that while an installation might initially be determined to have an uncluttered environment, subsequent introduction of new services may change this, so interference defenses are prudent even in a clean environment. A potentially undesirable side effect of tight pre-filters is the possible dispersion that can result from variable group delay across the filter passband. Thus it is important to include these criteria in selection of suitable pre-filters. The filters in the VP6000 LNA give rise to a maximum variation of 2 nanoseconds in group delay over the lower GNSS frequencies (from 1160 MHz to 1300 MHz) and 2.5 nanoseconds over the higher GNSS frequencies (from 1525 MHz to 1610 MHz). Also, the difference in group delay between the lower GNSS frequencies and the higher GNSS frequencies stays less than 5 nanoseconds.

The VP6000 series antennas are available with either a 35-dB gain LNA or with a 50-dB gain LNA for installations with long coaxial cable runs. The VP6000 is internally regulated to allow a supply voltage from 2.7 volts to 26 volts.

An interesting feature of the VP6000 is that the physical housing includes a secondary shielded PCB that is available for integration of custom circuits or systems within the antenna. This allows the addition of L1/L2 receivers for real-time kinematic operation, for example. A pre-filtered, 15-dB pre-amp version of the LNA is also available to provide RF input for OEM systems embedded within the antenna housing.

The VP6000 is available with a variety of connectors and with a conical radome to shed ice and snow and to deter birds for reference antenna installations. A precise and robust monument mount is also available.


In this article, we have described a research program that developed a series of CP antennas, which have increasingly improved performances directed towards GNSS applications. The resulting research CP prototype antenna has a very low cross-polarization, very low back radiation, very high phase-center stability and a compact structure. We have converted the research prototype into a commercially viable GNSS antenna with the superior electrical properties of the research prototype while building into the antenna the required physical ruggedness and manufacturability required of the commercial antenna.

With emerging satellite systems on the horizon, a new high-performance antenna is needed to encompass all GNSS signals. Our new antenna has sufficient bandwidth to receive all existing and currently planned GNSS signals, while providing high performance standards. Testing of the antenna has shown that the new innovative design (crossed driven dipoles associated with a coupled radiating element combined with a high performance LNA) has good performance, especially with respect to axial ratios, cross-polarization discrimination and phase-center variation.

These improvements make the antenna an ideal candidate for low-elevation-angle tracking. The reception of the proposed new signals along with additional low-elevation-angle satellites will bring new levels of positional accuracy to reference networks, and benefits to the end users of the data. With its compact size and light weight, the antenna has been designed and built for durability and will stand the test of time, even in the harshest of environments.


This article is based, in part, on the paper “The Evolutionary Development and Performance of the VeraPhase GNSS Antenna” presented at the 2016 International Technical Meeting of The Institute of Navigation held in Monterey, California, Jan. 25–28, 2016.

JULIEN HAUTCOEUR graduated in electronics systems engineering and industrial informatics from the Ecole Polytechnique de l’Université de Nantes, Nantes, France, and received a master’s degree in radio communications systems and electronics in 2007 and a Ph.D. degree in signal processing and telecommunications from the Institute of Electronics and Telecommunications of Université de Rennes 1, Rennes, France, in 2011. From 2011 to 2013, he obtained postdoctoral training with the Université du Québec en Outaouais, Gatineau, Canada. In 2014, he joined Tallysman Wireless Inc. in Ottawa, Canada, as an antenna and RF engineer.

RONALD H. JOHNSTON received a B.Sc. from the University of Alberta, Edmonton, Canada, in 1961 and the Ph.D. and D.I.C. from the University of London and Imperial College (both in London, U.K.) respectively, in 1967. In 1970, he joined the University of Calgary, Canada, and has held assistant to full professor positions and was the head of the Department of Electrical and Computer Engineering from 1997 to 2002. He became professor emeritus in the Schulich School of Engineering in 2006.

GYLES PANTHER is a technology industry veteran with more than 40 years of engineering, corporate management and entrepreneurial experience. He spent the first 20 years of his career in the semiconductor industry, first with Plessey in the U.K., then in Canada with Microsystems International. Panther co-founded and acted as engineering vice president and chief technology officer (CTO) for Siltronics, followed by SilCom and SiGem. In 2002, he founded startup Wi-Sys Communications, acting as president and CTO. He is now president and CTO of Tallysman Wireless, his fourth successful start-up, which was founded in 2009. Panther holds an honours degree in applied physics from City University, London, U.K.


To come, check back soon.

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User location takes center stage in new Android OS

By Steve Malkos, Google Android Location and Context Group

Raw GNSS measurements from Android phones. Yep, they are coming. At Google we have been working with our GNSS partners to give application developers access to raw GNSS measurements from a phone.

This is really exciting, and marks a new era for our GNSS community. At Google I/O in May, we announced that raw GNSS measurements are available to apps in the Android N operating system, which will be released later this year. This means you can get pseudoranges, Dopplers and carrier phase from a phone or tablet.

When can you get it? Well, it will take some time to proliferate throughout the ecosystem, but the first phone that will provide raw measurements will be the Nexus phone that we will launch later this year, and then next year you will see new Android handsets start to support it, as it will become a mandatory feature in Android.

Tutorial. At the Institute of Navigation’s ION-GNSS+ conference this September, Frank van Diggelen and I will teach a tutorial where you can learn to access and use these raw measurements. This will be a hands-on course where you collect, view and process raw measurements. You will leave the class with the data, Google software tools, and the knowledge of how to use them.

This tutorial is open only to ION-GNSS+ attendees. To register for the conference, visit www.ion.org/gnss/registration.cfm.

Then, to tailor this tutorial to your own needs, visit this online form and let us know what you’d like us to cover in the class.

The keynote presentation at Google I/O 2016, held May 12-20 at Shoreline Amphitheater in Mountain View, California.

The keynote presentation at Google I/O 2016, held May 12-20 at Shoreline Amphitheater in Mountain View, California.

More from Google I/O

Finally, I’d like to give you some highlights from Google I/O, the annual developer-focused conference held by Google in the San Francisco Bay Area.

During the keynote, Google CEO Sundar Pichai made many references to location, context and places. This was really exciting to see. We are innovating and working on a lot. It is amazing, even to me, after more than 13 years in the field of location, arriving at Google just under two years ago, to see how location and a user’s context are at the center of our connected world.

At Google, we are exposing as much as we can to the ecosystem so that innovation can thrive around us.

Sundar Pichai’s keynote address shows that user’s location is at the center for the knowledge graphs that we are building.

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Conversational examples were shown on Google Assistant and on how it can be used to get things done in the world. Sundar spoke on how location and context are the key to this future, noting that a user standing next to a famous sculpture can simply ask: “Who designed this?”

All Google I/O talks from the Android Location and Context Team can be found at these YouTube links :

STEVE MALKOS is the technical program manager in Google’s Android Location and Context Group. Before his role at Google, he worked as an associate program management director at Broadcom, where he managed engineering teams within Broadcom’s GNSS software.

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Sponsored by: NavCom
Broadcast date: Thursday, January 15, 2015
On-Demand Available Until: Friday, January 15, 2016
Moderator: Alan Cameron, Group Publisher, GPS World and Geospatial Solutions
Speaker: Greg Turetzky, Principal Engineer at Intel
Summary: The compound annual growth rate of GNSS devices will continue, from its current 22 percent level to a robust 9 percent for the years 2016–2022, and heading for seven billion installed units by 2022. The design challenges for GNSS are to:

  • Take advantage of smaller geometries to achieve higher clock speeds, more memory, lower active power and smaller size, while reducing standby power from leakage;
  • Incorporate new methodologies in chip and system design; integrate multiple radios on a single die to reduce cost and size;
  • Integrate multiple radio sources into a single location solution;
  • Bring together a disparate value chain.

The technology roadmaps embrace most modalities of positioning: GNSS, Bluetooth, Wi-Fi, cellular, and SBAS, and cross most platforms, including wearables.

Register now to learn how SiRFusion will enable new services, applications and social media for you.

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Eleven multiple-choice questions, how long can that take?  Tell us what you think about our magazine makeover for the last eight months.

visa-gift-cardTake a quick survey on GPS World’s recent redesign, and share your thoughts on our updated content and sections.

We’re even giving away $100 Visa gift cards to two randomly selected participants — just complete survey to be entered.

Click here to take part in the survey.

Thank you for your time!

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Alaska. “The Last Frontier” is a fitting slogan for this great land. The rugged terrain and harsh winters make an environment that only the bravest inhabitants can stand. Here, one of the latest surveying battles is being fought; not between land owners, but within the professional surveying community itself and pitting technology against historical tradition.

In the beginning…

The United States agreed to purchase Alaska from Russia in 1867 for $7.2 million dollars, or about two cents an acre. In 1959, Alaska, with a land mass larger than Texas, California and Montana combined, became the 49th state in the union.

For the professional surveyor, more than 20 million acres of federal government land is scheduled to be measured and divided for conveyance to the state for eventual sale to private individuals.

Surveying can be a challenging profession, and creating new townships in Alaska is no exception. In addition to the difficult environmental conditions, new procedural and technological advances are contesting historical means and methods of the creation of newly surveyed township tracts. The two main items are:

  • establishing coordinate values at corners instead of setting monuments.
  • GNSS and potential issues with atmospheric interference and lack of satellite coverage.

We will discuss the challenges ahead for the future of surveying in Alaska and how it will affect parcel division. While it is too soon to know whether or not this will bottleneck sales of parcels to new landowners, it does bring many technical and procedural questions for surveyors to the forefront.

Challenging historical methods

From the early days of our new nation, surveyors from the Bureau of Land Management (BLM) followed long standing procedures and placed retraceable monuments at various intervals along township boundaries for tract establishment, with two mile intervals being the predominant length for parcels in Alaska. The position of these monuments are held by subsequent surveyors to retrace these tracts for the state or individual owners.

During the course of the original field surveys, crews tasked with establishment of the new corners will note natural and artificial features for reference to these new parcel lines. These features may be trees or forestry lines, streams and rivers, mountains or glaciers. Because of these environmental challenges, these surveys take a great deal of time and effort to traverse through the difficult Alaskan wilderness.

However, the physical act of performing the survey is the only way to establish accurate ties to features found along the way. Surveyors will establish permanent markers at the chosen intervals along the township lines with measurements to nearby features for future retracement. Once placed, the monument becomes a corner for the township parcel and its position holds over any distance or angular measurement to other monuments or reference ties.

Performing these surveys is very costly and takes a great deal of time, so finding ways to reduce the budgetary expenditure for this task has been a priority for the BLM. Modern equipment and technology has improved efficiency and cut down on some necessary manpower, but it still takes a significant number of people to traverse through the dense areas of Alaska.

The BLM has proposed the following changes to establishment of township and section corners during property establishment through a system referred to as a “Direct Point Positioning Survey” (DPPS):

Implementation Direction: When preparing official surveys for areas of land selected by the State of Alaska pursuant to the Alaska Statehood Act, exterior boundaries of the selection area will be shown on the official plat by combinations of dependent resurvey, incorporation of record surveys where closure is met, and original survey. For original surveys, all angle points along the exterior boundary of the selection area shall be marked on the ground with a physical monument and shown on the official plat by reported coordinate and reference relationship to the NSRS datum and existing control stations. When deemed appropriate and directed in the Survey Special Instructions, other corner positions along, or internal to, the exterior boundary of the selection area can be reported and fixed by measure using reported coordinate and reference relationship to the NSRS datum and existing control stations and other marked corners of the survey with reported coordinates on the official survey plat. For surveys conducted using DPPS methods, if a corner is not marked with a physical monument, the geographic coordinate reported on the official survey record as fixing the corner location shall be accepted as the only evidence of the original corner position. For corners marked with a physical monument, the geographic coordinates reported on the official survey record shall be accepted as collateral evidence of the original corner position; the actual monumented location will remain the best evidence of the original corner position.

The BLM goes on to state the following conditions for implementation:

  • Ease of unofficial location of boundaries on the ground by using satellite positioning in mobile devices for groups like miners, oil and gas lessees, recreational users, prospective land owners, etc.
  • More economical future legal surveys when the need arises to mark the corners of property boundaries
  • A clear plan for future surveys that will allow efficient procedures for private land surveyors.
  • Reduced boundary uncertainty and costs due to monument destruction or disturbance.
  • Compatible and accurate boundary framework for GIS and other geospatial databases.
  • DPPS methods generate a greater certainty of comer positions and they are correct, consistent and repeatable.
  • DPPS methods introduce an economy of resources in the future for leaseholders and landowners when additional parcel boundary demarcation is required because geographic coordinates referenced to a known national datum are directly reported on the survey record and do not need to be calculated from the legacy measurement of bearings and distances.
  • Adoption of DPPS methods avoids spending substantial funds on unnecessary procedures like recovery, maintenance and rehabilitation of physical monuments in future survey work.
  • Surveys conducted using DPPS methods can be completed much more quickly than surveys completed using historical methods, thereby facilitating quicker patent to the State.

These new policies are reshaping not only how traditional surveyors perform their craft, but also flies in the face of more than 200 years of boundary establishment and case law determination of property rights. Surveyors follow a strict guide when evaluating evidence in legal descriptions and/or property boundaries:

Priority of Evidence Rules:

  1. Possessory Evidence
  2. Seniority of Title
  3. Documentary Evidence
    a. Call for a survey
    b. Call for monuments
    i. Natural
    ii. Artificial
    iii. Record
    c. Distance (or Direction)
    d. Direction (or Distance)
    e. Area
    f. Coordinates

Coordinates have historically always been the last resort for corner positioning and/or retracement use, yet the BLM feels that GNSS measurements have increased in reliability to a place where they can be more heavily relied upon for establishment of section corners and other significant points. This is where the second issue comes to light: positional accuracies using satellite-based measuring devices at high latitudes.

GNSS measurement and environmental challenges

For most of us “regular” surveyors in lower latitudes, our GPS/GLONASS measuring equipment operates with little to no trouble. Newer receivers are taking advantage of not only the U.S. and Russian satellites, but will eventually use the European Union Galileo satellites, China’s BeiDou, the Japanese QZSS and India’s IRNSS. Once these additional systems are operational, achievable accuracies worldwide will increase dramatically but we are still several years off.

The issues GNSS users in higher latitudes face are not only lack of satellite coverage, but several factors of environmental interference within the atmosphere. The result of these conditions and hazards are scintillation, positioning errors and cycle slips. These are very difficult to predict, thus increasing data-collection time and efforts to catch potential errors.

Scintillation occurs when rapid changes in amplitude and phase are observed and directly impacts the signal from the GNSS. Solar radio storms (caused by coronal mass ejection), large- and small-scale ionospheric structures (causing unpredictable values in environmental electrons) and geomagnetic activity (aurora) are also factors that affect signal, create cycle slips, and thus deteriorate the positional accuracy.

Studies performed by several technical teams (including NOAA/NGS) have shown that variations in position occurs often at CORS stations with little or no warning. Ongoing studies are helping to establish potential patterns in the atmospheric intruders, but will require much more analysis.

Some of these issues will be solved with more satellite coverage from the pending systems, but it will also require additional monitoring equipment to help forecast when potential environmental factors are about to occur. These systems will take time and money to develop, and thus increase the budgetary requirement for a new surveying procedure that was planned to save time and money.

But what does this all mean? From the historical side, placing monuments only at perimeter corners and not at township and section corners will place an extraordinary burden on future surveyors to “follow in the footsteps” of the original surveyor.

This flies directly against the duty of the retracement surveyor, so that alone will be a challenge. Studies have shown the instability of GNSS-derived accuracies as performed by highly trained scientists who are well educated at atmospheric recognition. Pairing a revised retracement procedure with providing GNSS-derived coordinate values with potentially faulty data instead of placing monuments is a recipe for disaster.

The biggest issue for most surveyors with implementation of the DPPS method will be for other jurisdictions to follow suit. The main priority of the surveyor is to protect the public. Making a change to allow coordinates to become acceptable evidence will lead to many more boundary disputes and court cases. Too often I hear that one surveyor thinks his coordinates are better than the next (myself included), yet we are dependent on what the receiver gets and the software calculates.

The surveyor tends to believe that GPS is “our” measuring device, and we have exclusive knowledge of its use and application, but we would be hard pressed to tell the client exactly what the equipment does to determine position and distance. A general understanding of your measuring tools is necessary, but it still comes back to knowledge of boundary law and the principles of how to apply them.

While I applaud the BLM for proposing a new procedure to help reduce costs for new original surveys in Alaska, I’m also afraid of the residual effect everywhere else as it establishes a new precedent.

So in the meantime, let the surveyors keep setting monuments and we will revisit the coordinate standard another day. And to quote the surveyor’s favorite geodesist, David Doyle: “Good coordination begins with good coordinates.” So let’s make sure we have accurate data.

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Sponsored by: NavCom
Broadcast date: Thursday, April 16, 2015
On-Demand Available Until: Friday, April 15, 2016
Moderator: Tracy Cozzens, Managing Editor, GPS World and Geospatial Solutions
Speakers: Gian Gherardo Calini, Head of Market Development, European GNSS Agency; Justyna Redelkiewicz Musial, Market Development Officer, European GNSS Agency; Peter Grognard, Director, Thales Alenia Space Belgium
Summary: The fourth edition of the European GNSS Agency’s (GSA’s) GNSS Market Report is now available. The Report has become a key reference for organizations building their GNSS market strategies. Join us as we provide an overview of the report and its quantification of the GNSS market of today and the future. We’ll specifically look at the global GNSS market in terms of shipments, revenues and installed base of receivers, with a forecast up to 2023.
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Sponsored by: NavCom
Broadcast date: Thursday, June 18, 2015
On-Demand Available Until: Friday, June 17, 2016
Moderator: Alan Cameron, Editor-In-Chief and Publisher, GPS World
Speakers: John Fischer, Chief Technology Officer, Spectracom; Lisa Perdue, Applications Engineer, Spectracom; Hironori Sasaki
Director of Solutions Architecture, Spectracom
Summary: Advanced driver-assistance systems (ADAS) are now integrated in all luxury cars and moving into mainstream models. Although no driverless car is expected to operate freely on public roads for the next 10 years, some open test drives have already taken place, including one 100-mile highway cruise by a driverless Mercedes. This technology is currently restrained by legal issues and the lack of reliable nationwide mapping data — but the platforms are nearly ready to go. Join us as we explore the current state of affairs and the likely near-term future developments.
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